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[PATCH] configfs: Fix failing symlink() making rmdir() fail

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On a similar pattern as mkdir() vs rmdir(), a failing symlink() may make rmdir()
fail for the symlink's parent and the symlink's target as well.

failing symlink() making target's rmdir() fail:

	process 1:				process 2:
	symlink("A/S" -> "B")
	  allow_link()
	  create_link()
	    attach to "B" links list
						rmdir("B")
						  detach_prep("B")
						    error because of new link
	    configfs_create_link("A", "S")
	      error (eg -ENOMEM)

failing symlink() making parent's rmdir() fail:

	process 1:				process 2:
	symlink("A/D/S" -> "B")
	  allow_link()
	  create_link()
	    attach to "B" links list
	    configfs_create_link("A/D", "S")
	      make_dirent("A/D", "S")
						rmdir("A")
						  detach_prep("A")
						    detach_prep("A/D")
						      error because of "S"
	      create("S")
	        error (eg -ENOMEM)

We cannot use the same solution as for mkdir() vs rmdir(), since rmdir() on the
target cannot wait on the i_mutex of the new symlink's parent without risking a
deadlock (with other symlink() or sys_rename()). Instead we define a global
mutex protecting all configfs symlinks attachment, so that rmdir() can avoid the
races above.

Signed-off-by: Louis Rilling <louis.rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
This commit is contained in:
Louis Rilling 2008-06-20 14:09:22 +02:00 committed by Mark Fasheh
parent 4768e9b18d
commit 9a73d78cda
3 changed files with 16 additions and 0 deletions
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1
fs/configfs/configfs_internal.h
View file

@ -51,6 +51,7 @@ struct configfs_dirent {
#define CONFIGFS_USET_IN_MKDIR 0x0200
#define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR)
extern struct mutex configfs_symlink_mutex;
extern spinlock_t configfs_dirent_lock;
extern struct vfsmount * configfs_mount;

10
fs/configfs/dir.c
View file

@ -1207,6 +1207,11 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
return -EINVAL;
}
/*
* Ensure that no racing symlink() will make detach_prep() fail while
* the new link is temporarily attached
*/
mutex_lock(&configfs_symlink_mutex);
spin_lock(&configfs_dirent_lock);
do {
struct mutex *wait_mutex;
@ -1215,6 +1220,7 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
if (ret) {
configfs_detach_rollback(dentry);
spin_unlock(&configfs_dirent_lock);
mutex_unlock(&configfs_symlink_mutex);
if (ret != -EAGAIN) {
config_item_put(parent_item);
return ret;
@ -1224,10 +1230,12 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
mutex_lock(wait_mutex);
mutex_unlock(wait_mutex);
mutex_lock(&configfs_symlink_mutex);
spin_lock(&configfs_dirent_lock);
}
} while (ret == -EAGAIN);
spin_unlock(&configfs_dirent_lock);
mutex_unlock(&configfs_symlink_mutex);
/* Get a working ref for the duration of this function */
item = configfs_get_config_item(dentry);
@ -1517,11 +1525,13 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
mutex_lock_nested(&configfs_sb->s_root->d_inode->i_mutex,
I_MUTEX_PARENT);
mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
mutex_lock(&configfs_symlink_mutex);
spin_lock(&configfs_dirent_lock);
if (configfs_detach_prep(dentry, NULL)) {
printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n");
}
spin_unlock(&configfs_dirent_lock);
mutex_unlock(&configfs_symlink_mutex);
configfs_detach_group(&group->cg_item);
dentry->d_inode->i_flags |= S_DEAD;
mutex_unlock(&dentry->d_inode->i_mutex);

5
fs/configfs/symlink.c
View file

@ -31,6 +31,9 @@
#include <linux/configfs.h>
#include "configfs_internal.h"
/* Protects attachments of new symlinks */
DEFINE_MUTEX(configfs_symlink_mutex);
static int item_depth(struct config_item * item)
{
struct config_item * p = item;
@ -147,7 +150,9 @@ int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symna
ret = type->ct_item_ops->allow_link(parent_item, target_item);
if (!ret) {
mutex_lock(&configfs_symlink_mutex);
ret = create_link(parent_item, target_item, dentry);
mutex_unlock(&configfs_symlink_mutex);
if (ret && type->ct_item_ops->drop_link)
type->ct_item_ops->drop_link(parent_item,
target_item);